A standard flow-control valve such as described in German patent document 3,107,431 of W. Orszullok has a normally stationary housing in which is provided a fixed valve plate formed with at least one throughgoing outlet port and a control plate formed with an inlet port. The control plate can be moved into a position with the inlet port at least partially in registration with the outlet port for flow from the cavity into the outlet port.
A common problem with such a system is that flow through the valve in the open condition exerts a torque or lateral force on the control plate and, when pressure is high enough, this force can be sufficient to move the control plate and change the valve's setting. Furthermore laterally deflected flow can strip lubricant off the finely machined meeting faces of the valve and control plates, and particles in the flow can even erode these surfaces.